Microelectronic devices are used in computers, communications equipment, televisions and many other products. Typical microelectronic devices include processors, memory devices, field emission displays and other devices that have circuits with small, complex components. In current manufacturing processes, the components of such circuits are generally formed on a substrate or a wafer with conductive, insulative, and semiconductive materials. Each substrate typically has 50-200 microelectronic devices, and each microelectronic device may have several million components. Accordingly, there is a significant drive in the microelectronic device industry to reduce the size and increase the density of components in integrated circuits.
As the density of components in integrated circuits increases, the highly conductive components of an integrated circuit need to be extremely small to provide enough space for the other components. Typical high conductivity components in integrated circuits include runners, damascene lines, contact plugs/vias, dual-damascene lines and other highly conductive components. To provide additional space for the other components of an integrated circuit, the major cross-sectional dimension of many highly conductive components is approximately 0.3 .mu.m or less. In several applications, the major dimension of highly conductive components is preferably 0.18 .mu.m or less.
Highly conductive components are formed on top of dielectric layers or in voids in dielectric layers. Conductive lines on top of a dielectric layer, for example, may be formed by depositing a conductive layer over the dielectric layer and then etching the conductive layer to electrically isolate conductors on top of the dielectric layer. Conductive components may also be formed in dielectric layers. For example, damascene lines are a type of conductive line fabricated by etching trenches in a silicon oxide layer down to a silicon nitride etch-stop layer, filling the trenches with a highly conductive material, and then planarizing the wafer down to the silicon oxide layer. Contact vias/plugs are another type of conductive component fabricated by etching vertical holes through a dielectric layer and filling the holes with a highly conductive material. Highly conductive components are generally composed of aluminum, copper or tungsten.
Although conventional conductive components perform adequately for many applications, highly conductive components are beginning to limit the performance of extremely high density integrated circuits with very small components because the resistance per unit length of long, narrow conductive lines is undesirably high. Aluminum is desirable for short or wide conductive features, but it is too resistive for use in long, narrow conductive components. Copper is more conductive than aluminum, but the resistance per unit length of copper conductive components may be too high for long, narrow conductive lines because copper loses an electron to surrounding silicon and silicon oxide layers. To prevent copper molecules in damascene lines from losing an electron to the surrounding silicon oxide layer, the trenches are lined with a barrier layer. However, the barrier layer reduces the cross-sectional area of copper damascene lines thereby exacerbating the problem of high resistance per unit length. Tungsten is also used for conductive components, but it is difficult to fill small voids in dielectric layers with tungsten. Accordingly, aluminum, copper and tungsten conductive lines are not well suited for high density integrated circuits with long, narrow conductive lines having a width of 0.3 .mu.m or less.